﻿/*
  KeePass Password Safe - The Open-Source Password Manager
  Copyright (C) 2003-2017 Dominik Reichl <dominik.reichl@t-online.de>

  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Text;

using KeePassLib.Resources;

namespace KeePassLib.Cryptography.Cipher
{
  public sealed class ChaCha20Engine : ICipherEngine2
  {
    private static PwUuid m_uuid = null;

    internal static PwUuid ChaCha20Uuid
    {
      get
      {
        PwUuid pu = m_uuid;
        if (pu == null)
        {
          pu = new PwUuid(new byte[] {
                        0xD6, 0x03, 0x8A, 0x2B, 0x8B, 0x6F, 0x4C, 0xB5,
                        0xA5, 0x24, 0x33, 0x9A, 0x31, 0xDB, 0xB5, 0x9A });
          m_uuid = pu;
        }

        return pu;
      }
    }

    public PwUuid CipherUuid
    {
      get { return ChaCha20Uuid; }
    }

    public string DisplayName
    {
      get
      {
        return ("ChaCha20 (" + KLRes.KeyBits.Replace(@"{PARAM}",
            "256") + ", RFC 7539)");
      }
    }

    public int KeyLength
    {
      get { return 32; }
    }

    public int IVLength
    {
      get { return 12; } // 96 bits
    }

    public Stream EncryptStream(Stream sPlainText, byte[] pbKey, byte[] pbIV)
    {
      return new ChaCha20Stream(sPlainText, true, pbKey, pbIV);
    }

    public Stream DecryptStream(Stream sEncrypted, byte[] pbKey, byte[] pbIV)
    {
      return new ChaCha20Stream(sEncrypted, false, pbKey, pbIV);
    }
  }

  internal sealed class ChaCha20Stream : Stream
  {
    private Stream m_sBase;
    private readonly bool m_bWriting;
    private ChaCha20Cipher m_c;

    private byte[] m_pbBuffer = null;

    public override bool CanRead
    {
      get { return !m_bWriting; }
    }

    public override bool CanSeek
    {
      get { return false; }
    }

    public override bool CanWrite
    {
      get { return m_bWriting; }
    }

    public override long Length
    {
      get { Debug.Assert(false); throw new NotSupportedException(); }
    }

    public override long Position
    {
      get { Debug.Assert(false); throw new NotSupportedException(); }
      set { Debug.Assert(false); throw new NotSupportedException(); }
    }

    public ChaCha20Stream(Stream sBase, bool bWriting, byte[] pbKey32,
        byte[] pbIV12)
    {
      if (sBase == null) throw new ArgumentNullException("sBase");

      m_sBase = sBase;
      m_bWriting = bWriting;
      m_c = new ChaCha20Cipher(pbKey32, pbIV12);
    }

    protected override void Dispose(bool bDisposing)
    {
      if (bDisposing)
      {
        if (m_sBase != null)
        {
          m_c.Dispose();
          m_c = null;

          m_sBase.Close();
          m_sBase = null;
        }

        m_pbBuffer = null;
      }

      base.Dispose(bDisposing);
    }

    public override void Flush()
    {
      Debug.Assert(m_sBase != null);
      if (m_bWriting && (m_sBase != null)) m_sBase.Flush();
    }

    public override long Seek(long lOffset, SeekOrigin soOrigin)
    {
      Debug.Assert(false);
      throw new NotImplementedException();
    }

    public override void SetLength(long lValue)
    {
      Debug.Assert(false);
      throw new NotImplementedException();
    }

    public override int Read(byte[] pbBuffer, int iOffset, int nCount)
    {
      if (m_bWriting) throw new InvalidOperationException();

      int cbRead = m_sBase.Read(pbBuffer, iOffset, nCount);
      m_c.Decrypt(pbBuffer, iOffset, cbRead);
      return cbRead;
    }

    public override void Write(byte[] pbBuffer, int iOffset, int nCount)
    {
      if (nCount < 0) throw new ArgumentOutOfRangeException("nCount");
      if (nCount == 0) return;

      if (!m_bWriting) throw new InvalidOperationException();

      if ((m_pbBuffer == null) || (m_pbBuffer.Length < nCount))
        m_pbBuffer = new byte[nCount];
      Array.Copy(pbBuffer, iOffset, m_pbBuffer, 0, nCount);

      m_c.Encrypt(m_pbBuffer, 0, nCount);
      m_sBase.Write(m_pbBuffer, 0, nCount);
    }
  }
}
